Field of the Invention
The invention relates to a transmission device for a printing machine, more particularly, having an endless transmission element, rotating bodies around which the transmission element is wrapped, a tensioning device for tautening the transmission element, and an actuating device for displacing a first one of the rotating bodies parallel to the axis of rotation thereof.
A transmission device of this general type is disclosed, for example, in the published German Patent Document DE 44 23 286 A1. It is used to drive a supplemental roller of a printing unit in which, in a first operating state, there is contact between a printing plate carried by a plate cylinder and the additional roller and, in a second operating state, there is contact between an inking-unit roller and the supplemental roller. The supplemental roller is carried by an actuating device by which it is possible to change the operating states while performing a displacement of the supplemental roller parallel to the axis of rotation of the supplemental roller. The tensioning device which is provided for tautening the transmission element acts upon the slack side of the transmission element and has a tensioning roller which is prestressed under spring force in the direction of the slack side and rolls on the latter.
In the case of the foregoing heretofore known transmission device, the transmission element is always tautened, and indeed, independently of which of the operating states the printing unit is in, that is to say, irrespective of what position the axis of rotation of the supplemental roller is in.
Transmission devices intended for other purposes are disclosed, for example, in the published European Patent Document WO 95/01930. These transmission devices, respectively, are formed of a pair of deflector rollers which are positioned with mutual axial spacing. A respective pair of the deflector rollers has wrapped around itself a transmission element in the form of a revolving suction belt, which sweeps over a suction box and is thus used for the temporary guidance of a sheet that is placed on the transmission element and has been output from a printing unit of a printing machine. In this case, the circumferential speed of the transmission element depends upon the application of the respective transmission device; in one case this application is the pure transport of a sheet at machine speed and in another case the retardation of a sheet to a delivery speed. In the latter case, in particular, the transmission elements are subjected to a given amount of wear, so that these transmission elements have to be renewed at specific time intervals.
It is generally the case that, in the transmission devices cited, there are no increased demands on dimensional stability in relation to the length of the transmission elements. Slight deviations in this length are taken into account by providing a tensioning device with which tautening of the transmission element can be effected.
An appropriate tensioning device is not provided for the transmission devices disclosed in the aforementioned published European Patent Document WO 95/01930. In order to install suitably a tensioning device appropriate for the transmission device mentioned at the introduction hereto, a given amount of available installation space is necessary both between the sides or strands of the transmission element and outside the latter. In the case of the transmission devices according to the published European Patent Document WO 95/01930, there are relatively restricted spatial conditions both between the strands or sides and outside or beyond them, the spatial conditions being caused specifically, on the one hand, by a suction box arranged within the runs and, on the other hand, by the close proximity of at least one of the transmission devices to further constructional elements, such as floating guides in this case.